Other intangible assets (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 9,166,000	$ 12,296,000	$ 9,840,000
Amortization of intangible assets	700,000	800,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2015	2,500,000
2016	2,200,000
2017	1,900,000
2018	1,000,000
2019	900,000
Thereafter	1,400,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	20,975,000	21,310,000	21,310,000
Intangible assets, accumulated amortization	(15,649,000)	(14,230,000)	(15,556,000)
Intangible assets, net (excluding goodwill)	5,326,000	7,080,000	5,754,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	4,409,000	5,580,000	5,080,000
Intangible assets, accumulated amortization	(3,504,000)	(4,335,000)	(4,098,000)
Intangible assets, net (excluding goodwill)	905,000	1,245,000	982,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	8,300,000	10,920,000	10,921,000
Intangible assets, accumulated amortization	(5,365,000)	(6,949,000)	(7,817,000)
Intangible assets, net (excluding goodwill)	$ 2,935,000	$ 3,971,000	$ 3,104,000